On Monday morning, President Trump tweeted, “A big deal looking good with Mexico!” Later, he announced that a deal had been reached and seemed ready to declare victory. The problem with this, of course, is that U.S. trade policy, especially when enacted through legislation, does not simply bend to the president’s will, even when expressed forcefully from the Oval Office.

For a president who can claim few successes from his belligerent trade policies, an agreement with Mexico that would pave the way for revising and updating the North American Free Trade Agreement would be a key victory. The only problem is that, for Trump, even with his announcement, there are still roadblocks to renegotiating NAFTA: Congress and Canada.